This invention has relation to telescopic crane booms consisting of a plurality of nested boom sections. The outwardly extending section of each pair of mutually telescopic sections is situated inside of the inward section and, typically, today, supported to slide with respect to the inward, outside section under load at a front reaction point on the inward, outside section, and at a rear reaction point between the rear of the outwardly extending inside section and the inward, outside section. This invention has relation to an advantageous structure mounting slide pads at these front and rear reaction points and for mounting side slide pads to resist any turning moments between adjacent sections.
In the prior art structures as typified, for example, by U.S. Pat. No. 3,837,502 to John T. Hornagold, granted Sept. 24, 1974, slide pads have been short in longitudinal direction of the boom sections, and have so caused poor load distribution in the side plates of those boom sections. The short side plates have resulted in excessively high loadings of the side plates as the boom sections are moved relative to each other under load.
Further, the positioning of the slide pads has caused high bending loads in the cap plates and premature buckling failure in the bottom plates of the boom sections.
The ultimate strength of a boom in its fully extended condition is limited by the amount of overlap between the front reaction point and the rear reaction point. When the slide pads are elongated longitudinally of the boom, in order to get better load distribution into the side plates, the effective front and rear reaction points are moved toward each other, and the effective working length of the boom sections in thus reduced.
When under load, and even, to a certain extent, when only carrying their own weight, as the boom sections are extended with respect to each other, each section, and consequently the entire boom, deflect significantly in downward direction. This makes it imperative for the slide pads moving with one end of one boom section to be mounted in such a manner that they can pivot with respect to the adjacent boom section over which they are sliding in order that the load can be distributed through the slide pads uniformly. Before the present invention, the construction of such pivotal mountings for slide plates was of a nature to shorten the effective length of each boom section, in many cases.